Electric motors are an increasing occurrence in vehicular and industrial applications. Common electric motor applications rely upon a Pulse Width Modulated (PWM) inverter bridge switching circuit, controlling the current supplied to each phase of a motor by opening and closing switches, resulting in revolution of the motor. Changes in pulse duration affect the power supplied to the load. In an ideal circuit, multiple instances of the same component would be identical and noiseless, and the currents and voltages supplied would be predictable and reliable. In real-life applications, however, this is unlikely. Circuit components react to stimulus, operating environment, and construction variations in ways that can result in variations in performance among seemingly similar components, and switches are known to suffer from arcing and “bounce” which results in EMC emission. When a number of switches emitting EMC noise, especially local to one another, begin to do so at the same frequency, the noise is additive and can affect other electronic components via induction, wireless signal interference, and more.
Some applications for PWM frequency selection to prevent harmonic EMC emission rely upon additional circuit components or varied layouts, which can increase the size or complexity of the control circuit. Still others assign PWM frequencies but make changes constantly, without consideration of the overall operating environment or system.